Carbon Flux Through the Twilight Zone-
New Tools to Measure Change
Schematic showing links between
continuous remote sensing of surface ocean C uptake, twilight
zone flux and deep ocean flux that are the focus of our
current NSF funded project at Bermuda.
Building upon the success of our VERTIGO
project, we continue to work to improve our understanding of
how materials travel from the surface to the deep ocean. This
pathway is called the "Biological Pump" (see Image
1 below) which refers to the combined activities that lead
to a quick pathway for plant and animal debris (molts, fecal
pellets, loose aggregated material) to sink as marine "snow"
or a particle into the deep ocean (see Image
2 below). In the open ocean, this cycle is largely a biological
one, though in some settings, transport of material delivered
by dust may matter (TENATSO - Cape
Verde time series project).
The "twilight zone" is a region of low light below the ocean's
sunlit surface "euphotic" zone, and above the deep ocean boundary
(around 1000m or 3000 feet). It is in this mysterious layer
where most of the sinking particles of the world's ocean are
consumed by the animals that live at depth.
In a new project starting in late 2006, we are designing an
autonomous vehicle called the "Twilight Zone EXplorer" (TZEX)
(see Image 3 below) to sample the ocean
particle flux and make remote measurements in the twilight zone.
Beginning in 2007, we will be starting to sample on a monthly
basis at Bermuda, as part of the BATS
(Bermuda Atlantic Time-Series) program using our existing
particle flux collectors, the Neutrally Buoyant Sediment trap
(see Image 4 below).
Image 1.
The
biological pump and processes regulating the flux of particles
in the ocean. Carbon dioxide fixed during photosynthesis
by phytoplankton in the upper ocean can be transferred
below the surface mixed layer via three major processes:
i) passive sinking of particles, ii) physical mixing of
particulate and dissolved organic matter (DOM), and iii)
active transport by zooplankton vertical migration. The
sinking flux includes senescent phytoplankton, zooplankton
fecal pellets, molts and mucous feeding-webs (e.g., larvacean
houses) and aggregates of these materials. The sinking
particle flux decreases with depth as aggregates are fragmented
into smaller, non-sinking particles, decomposed by bacteria,
and consumed and respired by zooplankton. This remineralization
returns carbon and nutrients to dissolved forms. The structure
of the planktonic community affects the composition and
the sinking rates of particles. Particle size, form, density,
and the content of biogenic minerals affect sinking and
remineralization rates.
Image 2. Example of changes in fecal pellets from sediment traps at three depths in the subarctic North Pacific (K2). Note the primarily cylindrical copepod pellets at 150 m, the red, carnivore-produced pellets at 300 m, and the large, ellipsoid larvacean pellets at 500 m. (Wilson, Steinberg, and Buesseler, in prep.)
Image 3. Schematic of proposed Twilight Zone Explorer.
Image 4.
WHOI NBST system being deployed.
TZEX Project Website
This site material is developed for NSF project PIs and those
wishing to know a bit more about the details of the science,
investigators, find a copy of the proposal, papers and other
materials that are being generated.
Dehairs, F., A. de Brauwere and M. Elskens (2008). Organic Carbon in the Ocean's Twilight Zone. EOS, Transactions American Geophysical Union, 89 (38): doi:10.1029/2008EO380004.
The Twilight Zone An interview with Ken Buesseler on Episode 5 of Nature Publishing Group's Simply Science, part of Scitable: A Collaborative Learning Space for Science.
A Journey to the Ocean's
Twilight Zone (pdf)
A conversation with marine biogeochemist Ken Buesseler: A torrent
of particles rains down through the ocean's dimly lit regions,
providing food for organisms below and sequestering some heat-trapping
carbon dioxide from the atmosphere. A WHOI biogeochemist investigates
what makes it into the ocean's twilight zone and what makes
it out.
Swimming in the Rain (pdf)
Novel untethered vehicle catches 'marine snow' falling through
the sea: At first, critics said it shouldn't be done. Then
they wondered whether it could be done. Finally, WHOI scientists
and engineers built an innovative device to capture a fundamental
but still mysterious ocean phenomenon.
